An actuator of this type is known for example from DE 198 58 085 C1 and comprises an elongate piezoelectric actuator, the change in length of said actuator in the axial direction, which results with activation, being transmitted to a hydraulic servo valve of a fuel injector. For this purpose a base plate of the piezoactuator is actively connected via a lever transmission to an axially guided valve piston of the servo valve. The movement transmitted from the piezoactuator to the valve piston by means of the lever transmission is used in the fuel injector for opening and closing a fuel injection valve.
A fundamental advantage of use of a servo injection valve actuated by means of a piezoelectric actuator is that with a comparatively small stroke (in the μm range) of the piezoactuator an injection valve body stroke that is usually greater by a multiple can be attained independently thereof (hydraulic stroke transmission). In addition this results in the advantage that the movement of the injection valve body for opening and closing the injection passage is driven by the pressure of the fuel which is available anyway at a comparable pressure in the region of the injection valve for the purpose of injection into the combustion chamber. To activate the injection valve an actuator with a comparatively low stroke and comparatively low actuator force is therefore sufficient.
Actuators of this type have a limited life however. It has been found that this life depends on the installation environment of the actuator. In particular it should be assumed that with the presence of fuel such as diesel or petrol, or lubricants such as the engine oil of an internal combustion engine in the installation environment, the life is shortened owing to penetration of this “harmful” media into the housing interior.